Process for producing oxygen by the liquefaction and rectification of air



Jan. 9, 1951 P. w. GARBO 2,537,046 PROCESS FOR PRODUCING OXYGEN BY THELIQUEFACTION AND RECTIFICATION OF AIR Filed Feb. 24, 1949 2 n m a m T. ma a m WW 4 I Illlll UHF vm h lfl QNJ 1|- 2%- T KN. RR m, wl m IHIIHHI Nbmm HHI \& Q SQ 1 .q\ mmm HHHI & W N2 Patented Jan. 9, 1951 PROCESS FORPRODUCING OXiGEN BY THE LIQUEFACTION AND RECTIFICATION OF Paul W. Garbo,Freeport, N. Y asslgnor to Hydrocarbon Research, Inc., New York, N. Y.,a corporation of New Jersey Application February 24, 1949, Serial No.78,118

8 Claims. 1

This invention relates to the production of oxygen'by the liquefactionand rectification of air in a rectification'system comprising low andhigh pressure stages.

All temperatures herein are in degrees 'F., pressures in pounds persquare inch gauge, and percentages are by volume.

Oxygen processes are known which involve the flow of air under pressurethrough reversing exchangers in which the air recovers the cold contentof the outgoing products of rectification and the thus cooled air isintroduced'into the high pressure stage of the rectification system. In

such processes the air is thus cooled in the exchanger to a temperatureclose to its condensation point at the pressure existing in thereversing exchanger. The carbon dioxide present in the air is therebysubstantially completely removed therefrom and deposited in the flowpath in the exchanger through which the air flows. Periodically theflows of the rectification product and the air through the reversingexchanger are reversed through their respective flow paths. Therectification product stream then removes by sublimation the carbondioxide deposited in the exchanger, thus purging same.

It is an object of this invention to provide a process for producingoxygen in which improved purging of the exchanger takes place.

Another object is to provide such process in which disturbance of thefractionating conditions within the rectification system is minimized.

Other objects and advantages of this invention will be apparent from thefollowing detailed description thereof.

In accordance with this invention liquid from the high pressure stage ofthe rectification system is passed through at least the cold end of thereversing exchanger in indirect heat ex:- change relation with the airand/or rectification product passing therethrough. This liquid is causedto boil by the heat extracted from the gas stream or streams flowing inindirect heat exchange relation therewith and the, resultant vapors areexpanded to produce refrigeration which is employed to compensate forenthalpy losses and for heat leaks into the system.

A specific embodiment of this invention involves the passage of aircompressed to a pressure of 60 to 150, preferably 75 to 125, pounds persquare inch and at a temperature of 50 to 110 F., preferably 60 to 80F., through a reversing exchanger in indirect heat exchange relationwith a stream of rectification product, e. g., nitrogen, the air beingthus cooled to a temperature close to its condensation point. Thereversing exchanger may be of either the regenerative or of therecuperative type. The thus cooled air is then passed to the highpressure stage of the rectification system and preferably brought intointimate contact with the crude liquid oxygen maintained in the lowerportion of the high pressure column. The crude liquid oxygen, desirablyafter passage through a purification system which .eilects removal ofresidual carbon dioxide and any acetylene which may be present, isdivided into two streams. One, the major stream consisting of from 90%to 95% of the liquid collected at the bottom of the high pressurecolumn, is expanded and introduced as refiux into the low pressurestage. The other stream consisting of from 5% to 10% of the crude liquidoxygen collected at the bottom of the high pressure column is warmed byfiow through at least the cold end of the exchanger where the liquid isvaporized by heat exchange with the air and/or rectification productpassing therethrough. Preferably, a stream of vapor of substantially thesame composition as that of air and herein referred to as of essentiallyair composition, preferably withdrawn from the bottom portion of thehigh pressure stage, is employed as a carrier to effect introduction ofthe liquid into the exchanger. In this way droplets of the liquid areintroduced into and caused to flow through a substantial portion of theflow path for the liquid through the exchanger before completevaporization of the liquid is effected.

The resultant vapors admixed with astream of essentially air compositionare introduced into an expander. 0f the total stream fed to the expander10% to 25% by volume is derived from the liquid withdrawn from thebottom of the high pressure column. The remainder is a stream ofessentially air composition, preferably, also derived from the highpressure column. The stream which is introduced into the expander andexpanded to produce the refrigeration necessary to compensate forenthalpy losses and heat leaks into the system corresponds to from 15%to 35%, preferably 15% to 25%, of the amount of air fed to the process.The stream passing through the expander and thence introduced into thelow pressure column is usually at least 10% richer in oxygen thanordinary air, since, as

. pointed out above, from 10% to 25% of this stream is derived from thecrude liquid oxygen (generally about 35% to 40% oxygen purity) withdrawnfrom the bottom of the high-pressure column. As compared with priorprocedures in 3 which a portion of cooled-air is expanded and theexpanded air introduced into the low pressure column, the process ofthis invention, involving asit does the introduction of a vapor streamenriched in oxygen into the low pressure column.

results in less disturbance in the fractionating conditions within thelow pressure column.

In the drawing forming a part of this specification the single figureillustrates aticallv a preferred layout of apparatus for practicing theprocess of this invention. It will be understood, however, thisinvention may be carried out in other apparatus than that shown in thedrawing. For example, any dmired number of reversing exchangers may beused instead of the reversing exchanger shown in the drawing, each pairof reversing exchangers arranged in series may be replaced by one longexchanger, reversing exchangers of the regenerative type may be used inlieu of the reversing exchangers of the recuperative type illustrateddiagrammatically in the drawing and other rectification systems may beused in lieu of that shown in the drawing including, for example,rectification systems in which separate columns are used for the low andhigh pressure stages.

Referring to the single figure of the drawing II is a recuperative heatexchanger which may be of any well-known type. In the embodiment shownin the drawing it consists of two sections II and II. Section II isprovided with four fiow paths l3, l4, ll and It disposed in concentricrelationship in heat exchange relation with each other. Section I: isprovided with interior fiow path l1 and concentric paths is and IIdisposed in heat exchange relation with each other. The heat exchangerIt has in each of the paths suitable fins of heat conducting material,e. g., coper or aluminum, permittin rapid and efilcient heat exchangebetween the gaseous media fiowing therethrollsh.

For purposes of illustration and in th interests of simplicity, eachflow path is shown on the drawing as consisting of a single tube, theseveral paths being disposed concentrically. Actually. however, eachpath in each exchanger may comprise a multiplicity of tubes for fiowtherethrough. As the construction of the heatexchangerpersedoesnotformapartofthisinvention and as it may be of anywell known type, it is believed further description thereof is un- Pathit is connected with path I by line II and path lswithpath it byline.'Ihesepaths l8, I4 and I9, I! are the paths through which air andnitrogen fiow, the fiow of these two media through their respectivepaths being periodically reversed so that during one step of the processair fiows through paths I! and i3 and nitrogen through paths it and i4and upon reversal during the succeeding step air flows through paths Itand I4 and nitrogen through paths i and I3. Reversal offiow isaccomplished by suitably positioning the reversing valves 23, 24 whichmay be of any well known type. Valve 23 is disposed in the pipe linesystem consisting of air inlet pipe 25 leading into valve 23, nitrogenexit line it leading to any suitable point of nitrogen disposal and pipelines 21, II leadin to one end of paths. II and I. Lines 20 and leadfrom the fiow paths "and ll of section II tovalve It. Aline II leadsfrom valve 24 through a non-reversing exchanger 1! to the high pressurestage it of the rectification system It hereinafter described andnitrogen line It leads into valve :4.

Plowpathsllandilarethefiowpaths through which oxygen fiows. These pathsare interconnected by line 83. Flow path I1 is provided with an exitline 84 leading to a suitable point of oxygen storage or utilization andthe flow path II is provided with an inlet line 3|. Flow of oxygenthrough fiow paths II and i1 continues unidirectionally, i.- e., fiowthrough these fiow paths is not reversed.

Flow path It is the fiow path into which a portion of the crude liquidoxygen from the base of the high pressure column is introduced,preferably admixed with a gaseous carrier stream of essentially aircomposition. The liquid thus introduced is vaporized and the resultantoxygenenriched air stream is warmed by flow through path It in indirectheat exchange relation with the air, nitrogen and oxygen flowing throughtheir respective paths in section II. In this way the temperatureapproach between the temperature of the air leaving fiow path ll or II,as the case may be, and the temperature of the nitrogen entering one orthe other of these fiow paths is brought within the range of 5 to 10 F.,preferably 6' to 8 It, resulting in more efilcient purging of these fiowpaths. Flow path It is rovided with an inlet line it and an exit line 31assing to an expander 40, which may be a centrifugal expander or turbineof any well known type. A line 42 connects the expander with the lowpressure stage of the rectification system 43.

Rectification system 43 comprises a two-stage rectification column, thelower section 44 of which is operated at a pressure of about to 150pounds, preferably about to pounds, and the upper section 46 of which isoperated at a pressure of about 4 to 12 pounds, preferably at about 5 to8 pounds. This column, as is customary, is provided with rectificationplates of the bubble cap or other desired type. The lower section 44communicates with a condenser 48 which acts as a reboiler for the lowpressure stage II. Condenser ll has a liquid collecting shelf 41 disimmediately below the condenser for llecting liquid nitrogen. Pipe line48 leads from this shelf 41 to a non-reversin heat exchanger 4!. A lineIt provided with a pressure reducing valve ll leads from thenonreversing exchanger ll to the top of low pressure stage II.

Fromthebaseportionofthehighpressurestagellalinellleadstoalinetlcommunicating with a pair of liquidpurifiers 84. II. A line II is communicably connected with the oppositeends of the purifiers I, It. Line I! is provided with a pair of valvesl1 and It associated with purifier I4 and with a second pair of valvesIt, 0 associated with purifier ll. Line 60 is provided with a pair ofvalves ii, if associated with purifier H and a second pair of valves 83,ll associated with purifier ll. Only one of the purifiers l4, Illsplaced on stream during operation. For example, valva II, II, Cl and 03may be closed and valves BI and .2 opened so that fiow of crude liquidoxygen from line It takes place through purifier l4 and line ll.Simultaneously, purifier ll may be purged by passing a suitable purgemedium, e. g., nitrogen or air, through the open valve '4 into andthrough the purifier II and through open valve I. When purifier 86requires pur in valves ll, ll, .2 and M are closed and II, I! opened,thereby placing purifier II on stream. Purifier It may then be purgedbyopeningvalvestl andl'landpassingasuitable purge medium therethrough,as hereinabove described in connection with the purging of purifier 55.

Preferably each of the purifiers 54 and 55 consists of a bed 55 ofgranular silica gel adsorbent having superimposed thereon a iilter plate66 for effecting removal of carbon dioxide particles from the crudeliquid oxygen. This filter may be porous silicon carbide or porousmetal. The silica gel acts to adsorb the acetylene dissolved in thecrude liquid oxygen and the filter medium 55 to separate out the solidcarbon dioxide. The silica gel adsorbent and the filter disposed in eachof the purifiers 54 and 55 are preferably so proportioned that thefilter and adsorber both require purging at about the same time. Insteadof having the silica gel in one and the same unit with the filter 55, asshown in the drawing, separate units, one functioning to effect removalof acetylene and the other carbon dioxide from the liquid oxygen may beemployed and these units may be designed to permit purging of eachindependently of the other.

A line 61 leads from line 56 and is provided with two branches 51a and51b. Branch 51a leads to a non-reversing exchanger From exchanger 68 aline 59 having an" expansion valve therein leads to the low pressurestage 45 for introducing thereinto, as reflux, crude oxygen freed ofacetylene and carbon dioxide. Branch 61b is provided with a valve 510for controlling flow therethrough and communicates with line 36 leadinginto flow path l5. Thus from 10% to of. the crude liquid oxygencollected at the bottom of column 44 and freed of acetylene and carbondioxide is introduced through lines 51b and 35 into flow path II.

From the top of condenser 45 a line H provided with an expansion valve12 leads into nitrogen line 13 leading from the top of low pressurestage 45. Nitrogen line 12 leads into the nonreversing exchanger 49which is connected by a nitrogen line 13a with non-reversing exchanger68. Nitrogen line 32 leads from the exchanger '68 into reversing valve24.

A line 14 leads from the base of the high .pressure column 44 just abovethe body of crude liquid oxygen therein and communicates with a pair oflines 15 and 15. Line 15 is provided with a valve 15a and communicateswith line 31 leading into expander 40. Line 15 is provided with a valve76a for controlling flow therethrough and communicates with line 35.

The base portion of low pressure column 45 is provided with an oxygenline 11 having a valve Ila therein for controlling flow therethrough.Line 11 leads into a non-reversing exchanger 15 from which line 35 leadsinto the ozwgen flow path l5.

In the operation of the equipment shown in the drawing, air is admittedthrough line 25, and, as indicated by the full line valve settings,fiows through line 28, flow path It, line 2|, flow path l3 in indirectheat exchange relation with nitrogen flowing through fiow paths M and I5and I oxygen flowing through flow paths l5 and II. The air leaving flowpath it through line 29 is thus cooled to a temperature close to itscondensation point, at which temperature it enters valve 24 and fiowsfrom this valve through line it and non-reversing heat exchanger It, andpasses up through the body of crude liquid oxygen maintained at the baseof the high pressure stage 44. The air bubbles through this crude liquidoxygen which effects removal of entrained carbon dioxide and acetylenefrom the air.

A minor portion of the liquid scrubbed airstreemiswithdrawnfrcmthehighpressurecolumn 44 just above the body ofcrude liquid oxygen maintained therein through line I4 and is dividedinto two streams one of which passes through line 15 and the otherthrough line 15. Crude liquid oxygen is continuously withdrawn throughline 52, passed through one or the other of the purifiers 54, 55 whicheifect removal of the carbon dioxide and acetylene contained therein andthen flows through line 55 into line 51 where the thus purified liquidis divided into two streams. One the minor stream. consisting of from 5%to 10% of the liquid withdrawn from the high pressure column, flowsthrough line 51b into line where it mixes with the air stream flowingthrough line It which functions as a gaseous carrier for the liquid inits flow through fiow path It introducing the liquid into this flow pathin the form of mist or fine droplets. The remainder of the crude liquidoxygen passes through line 61a, exchanger 68 and line 59 and is flashedas it flows through expansion valve Ill into the low pressure stage 45.

The oxygen-enriched air fiowing through path I5 is warmed by the airfiowing in a countercurrent direction through fiow path It. The thuswarmed oxygen-enriched air flows through line 31 where it mixes with thestream of essentially air composition fiowing through line 15. Theresultant oxygen-enriched air stream enters expander 40 at a temperaturesuch that liquefaction of the air in the expander does not take place.The expanded air flows through line 42 into the low pressure stage 45 ofthe rectification system at an intermediate point 42!: therein.

Liquid nitrogen flows from shelf 41 through line 45 into exchanger 49where it is cooled by the nitrogen gas flowing through this exchanger.From this exchanger the cooled nitrogen fiows through line 55 andexpansion valve 5| where it is fiashed and thus further cooled andenters the top of low pressure stage 45 where it serves as refiuxliquid.

Gaseous nitrogen flows through line 13 into exchanger 49, thence throughline Ila into exchanger thence through line 32 through reversing valve24, line 35, flow paths l4 and i8, exiting through line 21, valve 23 andline 26. If desired, some nitrogen may be withdrawn from the highpressure stage 44 through line H, flashed as it flows through valve 12and mixed with the nitrogen stream flowing through line I3. In this wayincondensible gases tending to collect in the high pressure stage 44 maybe purged therefrom.

Product oxygen fiows continuously from the low pressure stage 45 throughline ll, exchanger 18 into line 35, fiow paths l5 and I1, exitingthrough line 34.

Upon reversal, which may take place every 3 to 15 minutes, as indicatedby the dotted line valve settings, air fiows from line 25 through valve23 into and through line 21, flow paths is and I4, while the nitrogenflows through fiow paths is and i9 and the oxygen flows through flowpaths l5 and II. No reversal of flow of the oxygen or of theoxygen-enriched air stream passing through fiow path It takes place. Thefiow of the various streams from the reversing valve 24 tothe'rectification system 43, as well as the fiow of the various streamshereinabove described, within the rectification system and from therectification system to the reversing valve 24 remains the same. on eachreversal, the nitrogen efi'ects removal by sublimation and evaporationof carduring bon dioxide condensible impurities of air, e. g., moisture.depositedjin exchanger the preceding step f the process.

Instead of passing crude liquid oxygen in a carrier gas of essentiallyair composition through fiow path ii and admixing additional such gasfrom line II with the vapor stream flowing through line 21 and expandingthis mixture in expander ll, only the crude liquid oxygen, preferablyafter removal of acetylene and carbon dioxide therefrom, may be passedthrough branch l'lb into line It and through flow path II where theliquid is vaporized. The resultant vapors are expanded in expander 40and the expanded vapors introduced into the low pressure column II at apoint substantially below point 42a where line 42 leads into the lowpressure column. Usually the expanded vapor thus produced will provideonly a portion of the refrigeration necessary to compensate for enthalpylosses and for heat leaks into the system- The remainder of therefrigeration necessary for this purpose, desirably, is provided byexpanding the gas stream of essentially air composition withdrawnthrough line It in a separate expander and introducing the expanded airinto the low pressure column 48 at a point somewhat above point 42a.Operating in this manner 10% to 25% of the total stream expended in bothexpanders is derived irom the crude liquid oxygen collected in thebottom of the high pressure column and the remainder from the airwithdrawn through line 14.

One example of the operation or the process of this invention inapparatus of the type shown in the drawing is described below. It willbe understood this example is given for purposes of exemplification onlyand the invention is not limited thereto.

This example refers to an oxygen plant operated in a locality where theatmospheric pressure is 14.7 pounds per square inch absolute. All

pressuresgiveaintheexampleareinpoundsper square inch gauge.

liirunderpressureofaboutsfipoundsandat a temperature of 60 F. issupplied to line II and fiows through valve 28. line 28, flow path ll,line 2!, flow path llrthe air is thus cooled to a temperature of 2'l4I". The air then flows through reversing valve 24, exchanger ll into thehigh preuure stage II, the air entering this high premure stage at apressure of about 83 pounds and at a temperature of 275 1'. The airbubbles through the body of crude liquid oxygen (containingapproximately oxygen) maintainedinthebaseofthehigh pressurestage underpressure of about 88 pounds and at a temperature of -276 1'.

Crude liquid oxygen is withdrawn continuously through line I and passesthrough one or the other of the purifiers 84, ll which effects theremoval of entrained carbon dioxide and acetylene. Of this crude liquidoxygen 1.3% fiows through line 01b at a temperature of 278 1''. intoline3i, and thence through flow path ll of exchanger section II issuingtherefrom into line 81 at a temperature of about -13 F. A stream ofessentially air composition is withdrawn through line 14 at atemperature of -2'16 F. and apressure of about 82.5 pounds and fiowsthrough line II into line 81 where it mixes with the oxygenenrichedstream flowing through this line and thus produces a mixed stream at apressure of about 82 pounds and a temperature of --242 1''. This mixedstream is expanded in expander ll producing an oxygen-enriched airstream (28.3%

oxygen content) at a temperature of -80l' 1'. andapressureofabout9.4poundswhichisintroduced into the low pressure stage 4| throughline 62 at 42c. Ofthe totalstreamfedtoexpander 4|, 14.6% is derived fromthe crude liquid oxygen collecting at the bottom of high Pressure columnandtheremainderisthestreamof essentially air composition withdrawn throuline ll. Of the total air introduced into the process, 21.8% is expandedin expander Al to produce the refrigeration necessary to compensateforenthalpylossesandheatleabintothe system.

The remainder (92.7%) of the crude liquid oxygen flows through linel'ls. exchanger It, line ll and through expansion valve 10 where it isfiashedtoenterthelowpressurestagellua vapor-liquid mixture at atemperature of about 305' I". and a pressure of about 9 pounds.

Nitrogen is drawn from shelf 41 of h h pre sure stage M at a temperatureof --283 1". throughlinellexchangerllandlineuami passed throughexpansion valve 8! into the top of low pressure stage ll at atemperature of about 3l3 I and a pressure or about 7.8 pounds.

Nitrogen at a temperature of 3l3 l". and a pressure of about 7.3 poundsfiows through line ls,iswarmedinexchangersllandtltoatemperature of -2821''. at which temperature and a pressure of about 6.5 pounds it flowsthrough valve 24, enters line 20 flowing through aths M and I8, exitmgthrough line 21, valve 22 and exit line 2 at a temperature oi 60' I".and at substantially atmospheric pressure.

Oxygen at a temperature of 288' F. and a pressure of about 10 poundsfiows through line 11 and exchanger II and enters fiow path II at atemperature of --282' I. In its fiow through fiowpaths II andlLtheoxygeniswarmedtoa temperature of I". at which temperature and:pressure of about 1 pound it exits through line Upon reversal. whichmay take place every five minutes, the air iiows through paths, II and Mof exchanger sections it and II, respectively, and the nitrogen throughpaths I3 and il. The fiowofthevariousstreamsisotherwisethesame ashereinabove described and the temperature and pressure conditions remainthe same. The nitrogen in its fiow through piths l2 and II removes bysublimation and evaporation the carbon dioxide and frost, if any,deposited in these pathsbytheairduringtheprecedingstepofthe process.Thus in the continued operation, the

nitrogen rectification product effects-removal of the carbon dioxide andfrost, if any, deposited in the path through which the air has passed inthe preceding step of the process.

In the operation of the process of this invention, it is preferred toeffect removal of both moisture and carbon dioxide in the'reversingexchanger through which the air is passed. It will be understood,however, that, if desired, the moisture may be removed from the air byany conventional means and dry air containing carbon dioxide passedthrough the exchanger or exchangers as hereinabove disclosed. In theevent dryairissuppliedtotheprocees,reversingvaive 21 may advantageouslybe moved to a position between exchanger sections l2 and II so thatreversalotthefiowofairandnitrogentakesplace only in exchanger section IIwherein the carbon dioxide is deposited by the air stream. Operation ofsuch an arrangement is carried out so that the temperature at the warmend of ex- 8,587,048 9 l changer section II is at least slightlyhigher-than not of rectification and thus cool the air to a thetemperature at which carbon dioxide begins temperature close to itscondensation point, peto deposit from the air stream. In general, theriodically ers the flow of air and rectificawarm end of this exchangershould be at a temtion product through their respective paths inperature above about -1B0 F. 4 5 the reversing exchanger so that uponeach of said The expressions "reversing th no of i and reversals therectification product substantially nitrogen" and "reversal are usedherein in th completely removes the carbon dioxide. deposited sensecommonly employed in this art, namely, to in he r ing exchanger duringthe prece n mean the switching of the flow of two streams, s o the procs. p n the thus cooled air for example, the air and the nitrogen oroxygen through a y of crude l quid o y en in he hi h rstreams, so thatupon each reversal? the air pressure stage of the rectification system,confiows through the path through which had pretinuously passing aportion or the crude liquid viously flowed the nitrogen or oxygen and thoxygen into and through at least the cold end of nitrogen or oxygenflows through t t said reversing exchanger in indirect heat ex. throughwhi h ha previously flowed t change relation with the air andrectification It will be noted that i th proces of t product passingtherethrough thus vaporizing vention liquid from the high pressure stageis said crude q d y en. expanding the resultant passed th h flo path toand 1 vaporized by vapors to produce refrigeration to compensate h at rd from t air stream flowin i'or enthalpy losses and heat leaks into theprocthrough or as the case may be C55, and introducing the expandedvapors into the trogen stream passing therethrough. The inhringmg thetemperature approach between the low pressure stage oi. therectification system.

exiting stream and t incoming nitrogen 3. A process for producing oxygenby the liquestream within the range of 5a to F" prefers, faction andrectification of air in a rectification my 0 to with consequentimprovement in system involving high and low pressure stages, thepurging oi the flow path It or II by the niwhich comprises Passingstream of under pressure through a path in a reversing exchangertroductioh of liquid from the high pressure stage to recover the coldcontent of the outgolng'nitrointo flow path I reduces the cmss sect1oha1area gen product of rectification and thus cool the air of the feed lineto this how path and of the how to a temperature close to itscondensation point, path itself, 1. e., the tubes o'r passages in theexperiodichuy reversing the flow of air and nitrochanger through whichthe hquid flows. -Fun gen rectification product through their respectivethermore, the use of such liquid results in better Paths in thereversing exchanger that 5 heat transfer conditions in the cold end ofthe each of said reversas the nitrogen substantially exchanger.Moreover, the expanded stream introduced into the/low pressure stage at42a is enriched in oxygen and hence causes less disturbance of thefractionating conditions within this stage than would the introductionof a stream of expanded air. i

Since certain changes may be made in carry- 0 ing out the aboveprocesses without departing from the scope of the invention, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in in the reversing exchanger duringthe preceding step of the process, passing the thus cooled air through abody of crude liquid oxygen in the high pressure stage of therectification system, continuously passing a portion of the crude liquidoxygen into and through at least the cold end of said reversingexchanger in indirect heat exchange relation with the air and-nitrogenrectification product passing therethrough thus vaporizing said crudeliquid oxygen, expanding the resultant vapors to produce refrigerationto coma :igig pensate for enthalpy losses and heat leaks into theprocess, and introducing the expanded vapors process for producingoxygen by the lime into the low pressure stage of the rectificationfaction and rectification of air in a rectification system column, whichcomprises, passing a stream of air 4 A process for producing oxygen bythe homei iz g ig z g faction and rectification of air in arectification c anger recover e con en an system involving low and highpressure stages,

going product of rectification and thus cool the which comprises passinga stream of under to a temperature close to its chhdehsahon pressurethrough a path in a reversing exchanger pomt' h h reversing the now airand to recover the cold content of the outgoing rectifiiahoh pmdhctthrough their respective stream or nitrogen rectification product andthus paths m h reversing exchanger that upon cool the air to atemperature closeto its coneach of ,sald reversals the rectificationpmduct densation point, periodically reversing the flow of substantiallycompletely removes the carbon air and nitrogen rectification productthrough oxide deposited in the reversing exchanger their respectivepaths in the reversing exchanger i preceding of the Process ihh'odhc' sothat upon each of said reversals the nitrogen mg the thus cooled airinto the rectification colsubstantially completely removes the carbonpassing liquid from, d rectification dioxide deposited in the reversingexchanger umn into and through at least the cold end of during thepreceding step of the process, passing d reversing exchanger in indirectheat the thus cooled air through a body of crude liqchange relation withthe air and rectification m oxygen in t high pressure stage of t recthProduct P n therethrough thus vaporizing fication system thus scrubbingsaid thus cooled d liq d. and xpa d the r s ltant vapors air with saidcrude liquid oxygen, withdrawing a to P odu refrigeratifln to pe e fo eminor portion oi. the crude liquid oxygenthalpy losses and heat leaksinto the process. scrubbed air, passing a minor portion of said 2. Aprocess for producing oxygen by the liquecrude liquid oxygen togetherwith said minor faction and rectification of air in a rectificationportion of the crude liquid oxygen-scrubbed air system involving highand low pressure stages, through at least the cold end of said reversingwhich comprises, passing a stream of air under exchanger in indirectheat exchange relation pressure through a path in a reversing exchangerwith the air and nitrogen rectification product to recover the coldcontent of an outgoing prodto passing therethrough thus vaporizing thecrude completely removes the carbon dioxide deposited.

1! liquid oxygen and producing a vapor stream enriched in oxygen.expanding the oxygen-enriched vapor. and introducing the expanded vaporinto the low pressure stage of the rectification system.

5. A process producing oxygen as defined in claim 4, in which the vaporstream enriched in oxygen is at least 10% richer in oxygen than ordinaryair.

8. A process for producing oxygen by the liquefaction and rectificationor air in a rectification system involving low and high pressure stages,which comprises, passing a stream or air under pressure through a pathin a reversing exchanger to recover the cold content 01' outgoingstreams of oxygen and nitrogen rectification products and thus cool theair to a temperature close to its condensation point, periodicallyreversing the fiow of air and nitrogen rectification product throughtheir respective paths in the reversing exchanger so that upon each orsaid reversals the nitrogen substantially completely removes the carbondioxide deposited in the reversing exchanger during the preceding stepof the process, passing the thus cooled air through a body of crudeliquid oxygen in the high pressure stage of the rectification systemthus scrubbing said thus cooled air with said crude liquid oxygen,withdrawing a minor portion of the crude liquid oxygen-scrubbed air,dividing said minor portion into two streams, continuously passing crudeliquid oxygen from said body through a purification system which eflectsremoval of carbon dioxide from said crude liquid oxygen, dividing thepurified crude liquid oxygen into two streams, expanding one of saidstreams and introducing the expanded stream as reflux into said lowpressure stage, mixing the other liquid stream with one of the said'twostreams of crude liquid oxygen-scrubbed air, passing the re sultantmixture through at least the cold end of said reversing exchanger inindirect heat exchange relation with the air and nitrogen rectificationproduct passing therethrough thus vaporizing the crude liquid oxygen andproducing a vapor stream enriched in oxygen, mixing the other of saidtwo streams of crude liquid oxygenscrubbed air with the oxygen-enrichedvapor stream, expanding the resultant mixture, and introducing theexpanded mixture into the low pressure stage oi the rectificationsystem.

7. A process of producing oxygen by the lique (action and rectificationof air in a rectification system involving a low pressure stage and ahigh pressure stage, which comprises, passing a stream of air under apressure or from 60 to 150 pounds per square inch gauge and at atemperature of from 50 to 110 1". through a path in a reversingexchanger to recover the cold content or an outgoing stream of nitrogenproduct oi. rectification and thus cool the air to a temperature closeto its condensation point, periodically reversing the fiow of air andnitrogen rectification product through their respective paths in thereversing 12 exchanger so that upon each of said reversals the nitrogensubstantially completely removes the carbon dioxide deposited in thereversing exchanger during the preceding step in the process.passingthethuscooiedairthroushabodyoi crude liquid oxygen in the highpressure stage oi the rectification system thus scrubbing said thuscooled air with said crude liquid oxygen, withdrawing a minor portion ofthe crude liquid l0 oxygen-scrubbed air, dividing said minor portioninto two streams, continuously passing the crude liquid oxygen from thehigh pressure stage through a purification system which efiects removalof carbon dioxide from said crude liquid is oxygen, dividing the thuspurified crude liquid oxygen into two streams. one consisting ofapproximately 90% to 95% or the crude liquid oxygen and the otherconsisting of from 5% to expanding the stream consisting of from 90% to95% of the crude liquid oxygen to a pressure of from 4 to 12 pounds persquare inch gauge, introducing the expanded stream as reflux into saidlow pressure stage, mixing the stream consisting of from 5% to 10% ofthe crude liquid oxygen with one of the said two streams of crude liquidoxygen-scrubbed air. passing the resultant mixture through at least thecold end or said reversing exchanger in indirect heat exchange relationwith the air and nitrogen rectification product passing therethroughthus vaporizing the crude liquid oxygen and producing a vapor streamenriched in oxygen, mixing the other or said two streams oi crude liquidoxygen-scrubbed air with the oxygen-enriched vapor stream, expanding theresultant mixture to a pressure or from 4 to 12 pounds per square inchgauge, and introducing the expanded mixture into the low pressure stageof the rectification system.

8. A process for producing oxygen as defined in claim '7, in which from15% to 35% of the air introduced into the process is expanded to producethe refrigeration necessary to compensate for enthalpy losses and heatleaks into the process and of the total stream ted to the expander from10% to 25% is derived from the crude liquid oxygen collected in the highpressure stage.

PAUL W. GARBO.

REFERENCES CITED The following references are of record in the Name DateTrumpler Feb. 8, 1949 O'I'HERREFERENCES Air Purification in the RevisingExchanger, by hobo and Skaperdas, Transactions American In- Number 0stitute Chem. Engrs, Feb. 1947, P e 69.

Low Pressure Liquefaction or Air, by Rushton, Relrlgerating Engineering,Jan. 1947, page 24.

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATIONOF AIR IN A RECTIFICATION COLUMN, WHICH COMPRISES, PASSING A STREAM OFAIR UNDER PRESSURE THROUGH A PATH IN A REVERSING EXCHANGER TO RECOVERTHE COLD CONTENT OF AN OUTGOING PRODUCT OF RECTIFICATION AND THUS COOLTHE AIR TO A TEMPERATURE CLOSE TO ITS CONDENSATION POINT, PERIODICALLYREVERSING THE FLOW OF AIR AND RECTIFICATION PRODUCT THROUGH THEIRRESPECTIVE PATHS IN THE REVERSING EXCHANGER SO THAT UPON EACH OF SAIDREVERSALS THE RECTIFICATION PRODUCT SUBSTANTIALLY COMPLETELY REMOVES THECARBON DIOXIDE DEPOSITED IN THE REVERSING EXCHANGER DURING THE PRECEDINGSTEP OF THE PROCESS, INTRODUCING THE THUS COOLED AIR INTO THERECTIFICATION COLUMN, PASSING LIQUID FROM SAID RECTIFICATION COLUMN INTOAND THROUGH AT LEAST THE COLD END OF SAID REVERSING EXCHANGER ININDIRECT HEAT EXCHANGE RELATION WITH THE AIR AND RECTIFICATION